NEW YORK —
Newtown, Connecticut, residents laid wreaths and held prayer services Sunday as officials offered new details to the shooting. They said that 20-year-old Adam Lanza killed his mother, Nancy Lanza, shooting her four times in the head, and then drove to Sandy Hook Elementary School, where investigators believe he was once enrolled.

Carrying an assault rifle and two automatic handguns that had belonged to his mother, he shot his way in, firing bullets at school staff in the hallway and then at children and teachers in two classrooms. In less than ten minutes, twenty children, six and seven years old, and six women were killed.

Officials said Lanza brought enough ammunition to kill everyone in the school, but was interrupted. Connecticut Governor Dannel Malloy told ABC that Lanza committed suicide as police and other first responders arrived on the scene.

"We surmise that it was during the second classroom episode that he heard responders coming and apparently at that, decided to take his own life,” said Malloy.

President Obama Attends Connecticut Vigil

The massacre of children, one of 10 mass shootings in the U.S. in just the last two years, has stunned the country. Patty Boswell drove to Newtown from New York to share in the mourning.

"I can’t -- they are babies, they are just babies,” she said.

Recent Mass Shootings in the United States

July 2012: A gunman kills 12 people during a showing of Batman in Colorado.

January 2011: A gunman kills six people and wounds U.S. Representative Gabrielle Giffords in Arizona.

November 2009: A U.S. Army psychiatrist kills 13 people at Fort Hood, Texas.

April 2007: A Virginia Tech student kills 32 people before committing suicide.

April 1999: Two Columbine High School students kill 12 students, one teacher and themselves in Colorado.

"I think something has to be done," said Connecticut resident Yvonne Diallo who echoed the thoughts of many. "Something definitely has to be done. We can't live like this. This is worse than a third-world country. We can't ... they don't do this to their kids anywhere."

Her words were mirrored by President Obama, who came to Newtown Sunday night to participate in an interfaith service for the victims.

“We cannot tolerate this anymore," he said. "These tragedies must end, and to end them, we must change.”

The first funerals for the victims will take place Monday, with others scheduled for later in the week.